The Combustion Process

The combustion in fired heaters takes place in the burner. The types of burners and how they function are not covered in detail in this section. The amount of heat released can be easily calculated for a gas when we know the composition of the fuel and the heating values of the various components. For liquid fuels, the heating values are obtained by a calorimeter test.
From these values and using the standard combustion equation, we can determine the composition of the flue gas. As an example, the combustion of methane could be stated :

CH4 + 2O2 --- > CO2 + 2H2O
Of course for fuel gases containing many more components and burning in air rather than pure oxygen, the equation gets more complicated. Therefore, a task that in itself is quite simple, becomes a burden to do by hand, but can be easily accomplished by a simple computer program. The heating values normally used in fired heater design are the LHV, lower heating values.
To try some calculations, click the button below to open another window to do some fuel combustion calculations:

The following Lower Heating Values(LHV) are used in this script:
 Component Btu/lb Component Btu/lb Component Btu/lb CH4 21,520 C2H6 20,432 C3H8 19,944 N-C4H10 19,680 I-C4H10 19,629 N-C5H12 19,517 I-C5H12 19,478 C6H14 19,403 CO 4,347 H2 51,623 N2 0 CO2 0 C 14,093 S 3,983 C2H4 20,295 C3H6 19,691 C4H8 19,496 C6H6 17,480 H2O 0 O2 0 H2S 6,545